Borehole geophone repeatability experiment
Pietro (Peter) Giuseppe Gagliardi, Donald C. Lawton
Time-lapse vertical seismic profile data was obtained near Violet Grove, Alberta, using an array of eight 3-component geophones at depths between 1497 m to 1640 m. Baseline data were recorded in 2005 and the monitor recorded in 2007. Analysis of rotation angles was undertaken for both surveys, resulting in differences of less than 2 degrees for 54.2% in Line 2 and 85.9% in Line 3. Rotation angles were found to be more consistent at offsets greater than about 500 m. NRMS analysis gave averages of 61.4% and 45.3% for horizontal components, and 42.8% and 41.4% for the vertical component. Predictability analysis showed averages of 0.72 and 0.83 for horizontal components and 0.83 and 0.86 for the vertical component. In addition, traces were examined visually, and showed good qualitative repeatability. Since the receivers were cemented into place, the greatest effect on the repeatability was judged to be from small differences in the source locations between surveys, and differences in noise.